AVI - Audio Video Interleave

AVI stands for Audio Video Interleave. Microsoft introduced it in 1992 as part of Video for Windows, the software that first made video playback a normal thing for a desktop PC to do. For most of the following decade it was simply what a video file was on Windows, and enormous amounts of material were saved in it: camcorder tapes captured to disk, television recordings, early web downloads, screen captures. Newer containers have replaced it for everything current, but AVI files keep turning up whenever somebody opens an old hard drive or a folder of family clips.

How an AVI file is put together

AVI is built on RIFF, a general-purpose Microsoft structure that divides a file into labelled chunks. A header list describes the movie as a whole and each stream inside it, a large movi chunk holds the actual audio and video data in alternating pieces, and an index at the end lists where every piece begins so a player can jump around. The container itself does no compression. Each stream names its codec with a four-character code, and those codes are why old AVI files sometimes refuse to play: labels such as DX50 or XVID point at compression software the computer may no longer have installed.

Two design decisions age the format. AVI assumes a constant frame rate, expressed as microseconds per frame, so it has no natural way to store a variable frame rate or the per-frame timestamps modern phone video relies on, and audio drift is a familiar complaint. It was also built with a size ceiling that the later OpenDML extension had to work around so files could grow past a couple of gigabytes. AVI has no real support for chapters, and none for subtitles as a track, which is why subtitles for AVI films almost always arrive as a separate file next to the video.

What metadata an AVI file carries

This is the honest part: AVI carries very little. There is no equivalent of EXIF in an AVI, no standard place for a camera model and no standard place for GPS coordinates. What a report can tell you falls into two groups.

The technical facts come from the headers and are always present: width and height, frame rate, total frame count, duration, the number of streams, the codec code for each of them, and for audio the sample rate, the channel count and the bit rate.

Descriptive tags, when they exist at all, sit in an optional RIFF information chunk whose fields have four-letter names. The ones you are most likely to see are the title, the artist, a comment, the copyright notice, the genre, the subject, a creation date and the name of the software that wrote the file. Many AVI files have none of them. Some editing programs from Adobe embed an XMP packet, a structured text block holding title, author, copyright and editing history, in a chunk of their own invention. A few camera makers also added private chunks that general-purpose tools cannot name, so a report may list something it cannot interpret.

For you as a reader that mostly means good news and one caveat. An AVI is unlikely to be leaking your location or your device. But the software field and the creation date still say when the file was made and what made it, and any title or comment somebody typed years ago is still sitting in there.

When AVI still makes sense

Keep an AVI as it is when the file is an original you want to preserve unchanged, or when a piece of older software will only read that format. AVI is also still used for lossless capture, since a lossless codec inside an AVI produces a big file that has thrown nothing away.

For anything you want to watch, send or upload, MP4 is the practical replacement: far smaller at the same quality, playable everywhere, and able to hold the timing information AVI cannot. MKV is the better choice if the material has several audio languages or subtitle tracks you want inside one file. Converting means re-compressing, which costs a little quality, so keep the original if it matters to you.